The invention relates generally to lightwave communication systems and, more particularly, to an add/drop capability in dense wavelength division multiplexing systems.
Optical fiber has become the transmission medium of choice for communication networks because of the speed and bandwidth advantages associated with optical transmission. Wavelength division multiplexing (WDM), which combines many optical signals at different wavelengths for transmission in a single optical fiber, is being used to meet the increasing demands for more speed and bandwidth in optical transmission applications. With recent advances in optical networking technology, system manufacturers are now contemplating dense wavelength division multiplexing (DWDM) systems that carry, for example, as many as 40, 80, or more channels in a single fiber and with bit rates up to 10 Gbps per channel. In these DWDM systems, aggregate bandwidth in a single fiber is a function of the number of wavelength channels and the bit rate per wavelength channel.
DWDM is generally regarded as a channelized technology because a separate wavelength channel is allocated for carrying traffic from each source or user. Despite the many advantages of DWDM, the channelized nature of DWDM imposes limitations on transporting information in existing systems and networks. For example, wavelength exhaust becomes a problem because the number of users that can be supported by a DWDM system is limited by the number of available wavelengths. The total bandwidth in a DWDM system may also be used inefficiently if all wavelengths are not being used to transport information at the maximum possible bit rate.
In DWDM-based networks, the capability to selectively remove and add information carried by wavelength channels at multiple add/drop nodes across the network is essential for a variety of value-added communication services. For example, in many applications, such as telecommunications networks, optical LANs, and cable television subscriber systems, there may be a need to route one or more channels of a multiplexed optical signal to different destinations. An add/drop capability is especially important in networks that provide service to a large number of users with diverse traffic requirements, such as metropolitan area optical networks. In existing DWDM networks, add/drop functions are typically performed in a channelized manner wherein information is removed and inserted on a per-channel basis, i.e., each wavelength channel is separately managed.
In my co-pending U.S. application Ser. No. 09/237,122 which is herein incorporated by reference in its entirety, a DWDM transport scheme is proposed in which information is transported in a parallel format across a group of wavelength channels using a xe2x80x9cwavelength busxe2x80x9d architecture. As described in this co-pending application, the wavelength bus offers a more efficient use of bandwidth for transporting information in a DWDM system. However, conventional add/drop schemes which are based on a channelized approach cannot be used for removing and adding information transported in the wavelength bus.
The latency problems and bandwidth limitations of prior DWDM transport schemes are overcome and a configurable add/drop capability is provided according to the principles of the invention by transporting information in a parallel format using selected wavelength channels in a wavelength division multiplexed signal as a parallel bus (a xe2x80x9cwavelength busxe2x80x9d) and by selectively adding and dropping only information in the wavelength bus at an add/drop node. More specifically, one or more wavelength channels in a wavelength division multiplexed signal are allocated to form a wavelength bus for carrying multiplexed information supplied by one or more sources in a parallel format. At an add/drop node in the network, the wavelength channels in the wavelength bus are separated from the wavelength division multiplexed signal and information to be dropped is selectively removed by demultiplexing the parallel-formatted information. Information to be added at the add/drop node is multiplexed in a parallel format for transmission via the wavelength bus in the wavelength division multiplexed signal.
As compared to conventional, channelized DWDM transport schemes, a wavelength bus architecture has many advantages such as more efficient bandwidth utilization, reduced latency because of less serial-to-parallel and parallel-to-serial conversions, and sharing of resources among a group of wavelength channels, to name a few. Coupled with these advantages is a configurable add/drop capability wherein a wavelength division multiplexed signal can be partitioned into multiple wavelength buses so that one or more wavelength buses can be used for carrying information that is to be added and dropped at one or more nodes, while other information can be separately routed in the wavelength division multiplexed signal on a xe2x80x9cnormal throughxe2x80x9d basis. As such, a wavelength bus architecture with an add/drop capability is very adaptable and can support multiple users with different add/drop requirements at multiple nodes in a network.